Technical Field
This disclosure relates to a sheet conveying device that conveys a sheet, and an image forming apparatus such as a copier, printer, facsimile machine, a multi-functional apparatus including at least two functions of the copier, printer, and facsimile machine, and an offset printing machine.
Related Art
Known image forming apparatuses such as copiers and printers employ a sheet conveying device having a detector. As an example of the detector, the known sheet conveying device includes multiple CISs disposed at intervals in a sheet conveying direction along a sheet conveyance passage. Based on detection results of the multiple CISs, an angular displacement (skew) of a sheet (i.e., a positional deviation of a sheet in a radial or rotational direction) is corrected, and a lateral displacement of the sheet (i.e., a positional deviation of a sheet in a width direction that is a direction perpendicular to the sheet conveying direction) corrected to a normal position.
Specifically, a known image forming apparatus includes a pair of sheet holding rollers to rotate in the rotational direction or move in the width direction while holding and conveying a sheet. In addition, two CISs (a first detector) are disposed upstream from the pair of sheet holding rollers in the sheet conveying direction and aligned along the sheet conveyance passage and one CIS (a second detector) is disposed downstream from the pair of sheet holding rollers in the sheet conveying direction. These CISs are to detect an attitude of the sheet in the rotational direction and the width direction when the sheet is passing the respective positions of the CISs.
Then, while holding and conveying the sheet, the pair of sheet holding rollers 31 rotates in the rotational direction of the sheet to correct the angular displacement (skew) and moves in the width direction of the sheet to correct the lateral displacement based on the detection results detected by the two upstream side CISs. Thereafter, while holding and conveying the sheet after corrections of the angular displacement and the lateral displacement, the pair of sheet holding rollers further rotates in the rotational direction of the sheet to correct the angular displacement and moves in the width direction of the sheet to correct the lateral displacement based on the detection results detected by the two upstream side CISs disposed upstream from the pair of sheet holding rollers and the downstream side CIS disposed downstream from the pair of sheet holding rollers in the sheet conveying direction.
After having corrected the attitude of the sheet in the rotational direction and the width direction once while the pair of sheet holding rollers was holding and conveying the sheet, the above-described known sheet conveying device corrects for the second time (i.e., performs a recorrecting operation or a correcting operation of the angular and lateral displacements again). Therefore, the higher accurate correcting operation of the attitude of the sheet is greatly expected.
However, it is likely that the above-described known sheet conveying device cannot correct the attitude of the sheet with high accuracy when various sheets having different reflectance due to different colors are conveyed.